1. Field
One embodiment of the invention relates to a cache data-consistency assurance technology suitable for, for example, a disk system comprising one or more hard disk drive (HDD).
2. Description of the Related Art
Recently, computerization of work has been developed in various categories of business. It is common in office environments that each employee uses his/her personal computer (PC) for conducting business, and shared server computers connected to PCs via a local area network (LAN) are used for managing business data integratedly.
In a server computer used for the above purpose, it is important to ensure consistency of data that is read and written (and also updated) by a plurality of employees. Various inventions relating to mechanism for ensuring data consistency have been thus proposed so far (e.g., Jpn. Pat, Appln, KOKAI Publication No. 4-170625).
In a server computer used in the above purpose, a disk system in which, for example, increase in disk capacity with low cost is realized by providing a plurality of HDDs is often applied as an external storage device.
Also, recently, a PC mounting a solid-state drive (SDD), which employs a non-volatile semiconductor memory and serves as a recording medium, instead of an HDD has appeared. The SSD is faster in the data reading speed when compared with an HDD. Therefore, it is possible to improve response performance when a plurality of SSDs are used to configure a disk system. However, a disk system of this configuration becomes inevitably expensive and thus not practical.
As a compromise in consideration of cost, it may be also possible to improve response performance by configuring a disk system using, for example, both a HDD and an SSD and utilizing the SDD as a cache for the HDD. In this case, however, a new method for ensuring cache data consistency is required under circumstances in which the two types of storage device are controlled by different drivers depending on, for example, operation modes.